1. Field of the Invention
The present invention relates to bismuth precursor source compounds and compositions, and to a process for vapor phase deposition of bismuth-containing films on substrates utilizing such compounds and compositions.
2. Description of the Related Art
Bismuth-containing materials are useful for a number of applications, including, but not limited to, dielectric/ferroelectric SrBi.sub.2 Ta.sub.2 O.sub.9 (SBT), high temperature superconducting bismuth strontium calcium copper oxide (BSCCO) materials, and dielectric bismuth oxide films. Incorporation of bismuth into thin films for these and other applications has been problematic using conventional CVD precursors such as Bi(OEt).sub.3, BiPh.sub.3, Bi(thd).sub.3, etc. due to low volatility or limited thermal stability.
Accordingly, there is a need in the art for precursor compositions for deposition of bismuth to form bismuth-containing films and material layers.
Concerning known bismuth organometallic compounds, Clegg, et al., Inorg. Chem. 1991, 30, 4680-4682, discloses bismuth amides including Bi(NMe.sub.2).sub.3 and Bi(NPh.sub.2).sub.3 as bismuth amide compositions whose structure has been characterized by the authors. This article also states that apart from its potential usefulness as a precursor to bismuth chemistry in general, the dimethylamide bismuth compound disclosed in the article is extremely volatile and thus potentially valuable for chemical vapor deposition work. Other amides which have been reported include: Bi(NR.sub.2).sub.3 wherein R.dbd.Me, Et, n--Pr; Bi(N(SiMe.sub.3).sub.2).sub.3 ; Bi(N(Me)SiMe.sub.3).sub.3 ; Bi(Me).sub.2 (N(Me)SiMe.sub.3); BiCl.sub.2 (NEt.sub.2); BiBr.sub.2 (NMe.sub.2); BiI(NHR).sub.2 wherein R.dbd.n--Pr, n--Bu; and BiMe.sub.x (N(Me)SiMe.sub.3).sub.y wherein x=1, y=2 or x=2, y=1.
Among the various bismuth-containing films, bismuth-silicon-oxide films are potentially usefully employed for a variety of microelectronic and optoelectronic applications. Such bismuth-silicon compositions include sillenite, Bi.sub.12 SiO.sub.20, or BSO, a photorefractive material that is capable of high spatial resolution along with high speed switching and low switching energies.
BSO films find potential application as spatial light modulators (SLMs). SLMs are devices capable of modifying the amplitude, frequency, phase or polarization of an optical field. One or more of these properties is modulated when an intrinsic property of the SLM (e.g., refractive index, dielectric constant, absorbance, etc.) is altered by an externally applied electrical or optical signal. The ability of SLMs to modulate a two-dimensional optical wavefront can result in enormous signal processing enhancement and flexibility as compared with one-dimensional electronic modulation (see, for example, Neff, J. A., et al., "Two-Dimensional Spatial Light Modulators: A Tutorial," Proc. IEEE, 1990, 78, 826).
The central and varied roles of SLMs makes them pivotal for the development of future optical processing systems, and the use of SLMs in applications such as neural networks, sensors, flat panel displays, high speed interconnections and memory technologies. In fact, applications of one- and two-dimensional SLMs could encompass nearly every optical signal processing/computer architecture conceived.
Most commercial SLMs are based on liquid-crystal technology; while inexpensive, these devices have low contrast ratios, are relatively slow, and are subject to light scatter and non-uniformity.
In the fabrication of SLM devices using BSO, as well as other applications involving bismuth-containing thin films, the art continues to seek additional bismuth precursor compounds and compositions useful in the formation of such films.
Accordingly, it is an object of the present invention to provide improved compositions and methods for forming Bi-containing films on substrates.
It is another object of the present invention to provide improved bismuth precursors and method for making bismuth-containing SLM structures and devices.
It is a further object of the invention to provide precursors and method for forming bismuth oxide films on substrates.
It is yet another object of the invention to provide precursors and method for forming sillenite films on substrates.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.